This invention lies in the field of drilling rigs. More specifically, it is concerned with drilling rigs for drilling deep boreholes in the earth, such as for the production of oil and gas.
Still more particularly, this invention lies in the field of portable drilling rigs which can be broken down into small components for ease of transportation.
The invention concerns principally the design of the structural base for the drilling rig such that it has sufficient longitudinal rigidity, and still supports the mast, while in a horizontal position, at a level close to the top surface of the ground. Furthermore, it has a working table or floor, of requisite height, which supports the rotary table, and which is narrower than the base of the mast and can be positioned on the structural base either before or after the mast is in position, and whether the mast is in a lowered or a raised position. The table structure is broken into a plurality of parts, each of which are fitted into the structural base and can be assembled in a lowered position and then rotated and raised into the final operating position.
When the mast is in a raised position, additional support for the mast is provided by an A frame which is behind the mast and serves as a means for raising the mast by cable means over a pulley at the top of the A frame.
There is an additional feature of this invention which involves the support of the floor of the rig or the work table on which are mounted the rotary table, draw works, etc. In conventional designs such as illustrated in the Jenkins et al. U.S. Pat. No. 3,262,237, the floor is broken into two parts, one part of which is supported on the A frame and the other part of which is supported on the mast. When the mast is in a raised position, the two portions of the floor or table will match, providing a continuous surface. However, because of the break between the two portions of the table, the part of the table on which the rotary table is supported, which should be directly under the center line of the mast, must be supported off center on one or the other of the two tables.
In the prior art, there are many designs of drilling rigs of this general type, however, most of them have the tiltable or hinged mast, and A frame for raising the mast, supported on the work floor or table, which is part of a very large base structure, some 10-20 feet high. These masts terminate in two legs which rotate about shoes attached to the work floor on the top of the base structure. Masts, with two legs (rather than four legs as in this invention) must depend a large extent on lateral support from the A frame, which must be built stronger to provide this support.
Also, because of the two legs, the full weight on the crown block is supported at two points on the base structure supporting the mast. Thus the base structure must be designed to spread this force over a large area of the earth.
When the mast is hinged at the level of the working floor, which may be from 10-20 feet above the ground, and lowered to the ground, it is very difficult to assemble the parts of the mast on the ground and then raise the base end to the shoe supports on the working floor.